The present invention relates to devices and methods for measuring optical characteristics such as color spectrums, translucence, gloss, and other characteristics of objects such as teeth, and more particularly to devices and methods for measuring the color and other optical characteristics of teeth, fabric or numerous other objects, materials or surfaces with a hand-held probe that presents minimal problems with height or angular dependencies and that may be applied to detecting and preventing counterfeiting, and in particular devices and methods employing two stages of spectral separation.
A need has been recognized for devices and methods of measuring the color or other optical characteristics of teeth and other objects in the field of dentistry. There is also a need for devices and methods for detecting and preventing counterfeiting and the like based on measurements of various optical characteristics or properties of objects and materials. Various color measuring devices such as spectrophotometers and calorimeters are known in the art. To understand the limitations of such conventional devices, it is helpful to understand certain principles relating to color. Without being bound by theory, Applicants provide the following discussion. In the discussion herein, reference is made to an xe2x80x9cobject,xe2x80x9d xe2x80x9cmaterial,xe2x80x9d xe2x80x9csurface,xe2x80x9d etc., and it should be understood that in general such discussion may include teeth as well as other objects or materials as the xe2x80x9cobject,xe2x80x9d xe2x80x9cmaterial,xe2x80x9d xe2x80x9csurface,xe2x80x9d etc.
The color of an object determines the manner in which light is reflected from the object. When light is incident upon an object, the reflected light will vary in intensity and wavelength dependent upon the color of the object. Thus, a red object will reflect red light with a greater intensity than a blue or a green object, and correspondingly a green object will reflect green light with a greater intensity than a red or blue object.
The optical properties of an object are also affected by the manner in which light is reflected from the surface. Glossy objects, those that reflect light specularly such as mirrors or other highly polished surfaces, reflect light differently than diffuse objects or those that reflect light in all directions, such as the reflection from a rough or otherwise non-polished surface. Although both objects may have the same color and exhibit the same reflectance or absorption optical spectral responses, their appearances differ because of the manner in which they reflect light.
Additionally, many objects may be translucent or have semi-translucent surfaces or thin layers covering their surfaces. Examples of such materials are teeth, which have a complicated structure consisting of an outer enamel layer and an inner dentin layer. The outer enamel layer is semitranslucent. The inner layers are also translucent to a greater or lesser degree. Such materials and objects also appear different from objects that are opaque, even though they may be the same color because of the manner in which they can propagate light in the translucent layer and emit the light ray displaced from its point of entry.
One method of quantifying the color of an object is to illuminate it with broad band spectrum or xe2x80x9cwhitexe2x80x9d light, and measure the spectral properties of the reflected light over the entire visible spectrum and compare the reflected spectrum with the incident light spectrum. Such instruments typically require a broad band spectrophotometer, which generally are expensive, bulky and relatively cumbersome to operate, thereby limiting the practical application of such instruments.
For certain applications, the broad band data provided by a spectrophotometer is unnecessary. For such applications, devices have been produced or proposed that quantify color in terms of a numerical value or relatively small set of values representative of the color of the object.
It is known that the color of an object can be represented by three values. For example, the color of an object can be represented by red, green and blue values, an intensity value and color difference values, by a CIE value, or by what are known as xe2x80x9ctristimulus valuesxe2x80x9d or numerous other orthogonal combinations. For most tristimulus systems, the three values are orthogonal; i.e., any combination of two elements in the set cannot be included in the third element.
One such method of quantifying the color of an object is to illuminate an object with broad band xe2x80x9cwhitexe2x80x9d light and measure the intensity of the reflected light after it has been passed through narrow band filters. Typically three filters (such as red, green and blue) are used to provide tristimulus light values representative of the color of the surface. Yet another method is to illuminate an object with three monochromatic light sources or narrow band light sources (such as red, green and blue) one at a time and then measure the intensity of the reflected light with a single light sensor. The three measurements are then converted to a tristimulus value representative of the color of the surface. Such color measurement techniques can be utilized to produce equivalent tristimulus values representative of the color of the surface. Generally, it does not matter if a xe2x80x9cwhitexe2x80x9d light source is used with a plurality of color sensors (or a continuum in the case of a spectrophotometer), or if a plurality of colored light sources are utilized with a single light sensor.
There are, however, difficulties with the conventional techniques. When light is incident upon a surface and reflected to a light receiver, the height of the light sensor and the angle of the sensor relative to the surface and to the light source also affect the intensity of the received light. Since the color determination is being made by measuring and quantifying the intensity of the received light for different colors, it is important that the height and angular dependency of the light receiver be eliminated or accounted for in some manner.
One method for eliminating the height and angular dependency of the light source and receiver is to provide a fixed mounting arrangement where the light source and receiver are stationary and the object is always positioned and measured at a preset height and angle. The fixed mounting arrangement greatly limits the applicability of such a method. Another method is to add mounting feet to the light source and receiver probe and to touch the object with the probe to maintain a constant height and angle. The feet in such an apparatus must be wide enough apart to insure that a constant angle (usually perpendicular) is maintained relative to the object. Such an apparatus tends to be very difficult to utilize on small objects or on objects that are hard to reach, and in general does not work satisfactorily in measuring objects with curved surfaces. Such devices are particularly difficult to implement in the field of dentistry.
The use of color measuring devices in the field of dentistry has been proposed. In modem dentistry, the color of teeth typically are quantified by manually comparing a patient""s teeth with a set of xe2x80x9cshade guides.xe2x80x9d There are numerous shade guides available for dentists in order to properly select the desired color of dental prosthesis. Such shade guides have been utilized for decades and the color determination is made subjectively by the dentist by holding a set of shade guides next to a patient""s teeth and attempting to find the best match. Unfortunately, however, the best match often is affected by the ambient light color in the dental operatory and the surrounding color of the patient""s makeup or clothing and by the fatigue level of the dentist. In addition, such pseudo trial and error methods based on subjective matching with existing industry shade guides for forming dental prostheses, fillings and the like often result in unacceptable color matching, with the result that the prosthesis needs to be remade, leading to increased costs and inconvenience to the patient, dental professional and/or prosthesis manufacturer.
Similar subjective color quantification also is made in the paint industry by comparing the color of an object with a paint reference guide. There are numerous paint guides available in the industry and the color determination also often is affected by ambient light color, user fatigue and the color sensitivity of the user. Many individuals are color insensitive (color blind) to certain colors, further complicating color determination.
In general, color quantification is needed in many industries. Several, but certainly not all, applications include: dentistry (color of teeth); dermatology (color of skin lesions); interior decorating (color of paint, fabrics); the textile industry; automotive repair (matching paint colors); photography (color of reproductions, color reference of photographs to the object being photographed); printing and lithography; cosmetics (hair and skin color, makeup matching); and other applications in which it useful to measure color in an expedient and reliable manner.
While a need has been recognized in the field of dentistry, however, the limitations of conventional color/optical measuring techniques typically restrict the utility of such techniques. For example, the high cost and bulkiness of typical broad band spectrometers, and the fixed mounting arrangements or feet required to address the height and angular dependency, often limit the applicability of such conventional techniques.
Moreover, another limitation of such conventional methods and devices are that the resolution of the height and angular dependency problems typically require contact with the object being measured. In certain applications, it may be desirable to measure and quantify the color of an object with a small probe that does not require contact with the surface of the object. In certain applications, for example, hygienic considerations make such contact undesirable. In the other applications such as interior decorating, contact with the object can mar the surface (such as if the object is coated in some manner) or otherwise cause undesirable effects.
In summary, there is a need for a low cost, hand-held probe of small size that can reliably measure and quantify the color and other optical characteristics of an object without requiring physical contact with the object, and also a need for methods based on such a device in the field of dentistry and other applications.
In accordance with the present invention, devices and methods are provided for measuring the color and other optical characteristics of objects such as teeth, reliably and with minimal problems of height and angular dependence and which may be applied to detecting or preventing counterfeiting or the like. A handheld probe is utilized in the present invention, with the handheld probe containing a number of fiber optics in certain preferred embodiments. Light is directed from one (or more) light source(s) towards the object/tooth to be measured, which in certain preferred embodiments is a central light source fiber optic (other light sources and light source arrangements also may be utilized). Light reflected from the object is detected by a number of light receivers. Included in the light receivers (which may be light receiver fiber optics) are a plurality of perimeter and/or broadband or other receivers (which may be light receiver fiber optics, etc.). In certain preferred embodiments, a number of groups of perimeter fiber optics are utilized in order to take measurements at a desired, and predetermined height and angle, thereby minimizing height and angular dependency problems found in conventional methods, and to quantify other optical characteristics such as gloss. In certain embodiments, the present invention also may measure gloss, translucence and fluorescence characteristics of the object/tooth being measured, as well as surface texture and/or other optical or surface characteristics. In certain embodiments, the present invention may distinguish the surface spectral reflectance response and also a bulk spectral response.
The present invention may include constituent elements of a broad band spectrophotometer, or, alternatively, may include constituent elements of a tristimulus type colorimeter. The present invention may employ a variety of color measuring devices in order to measure color and other optical characteristics in a practical, reliable and efficient manner, and in certain preferred embodiments includes a color filter array and a plurality of color sensors. A microprocessor is included for control and calculation purposes. A temperature sensor is included to measure temperature in order to detect abnormal conditions and/or to compensate for temperature effects of the filters or other components of the system. In addition, the present invention may include audio feedback to guide the operator in making color/optical measurements, as well as one or more display devices for displaying control, status or other information.
With the present invention, color/optical measurements of teeth or the like may be made with a handheld probe in a practical and reliable manner, essentially free of height and angular dependency problems, without resorting to fixtures, feet or other undesirable mechanical arrangements for fixing the height and angle of the probe with respect to the object/tooth. In addition, the present invention includes methods of using such color measurement data to implement processes for forming dental prostheses and the like, as well as methods for keeping such color and/or other data as part of a patient record database.
In accordance with one preferred embodiment, a two stage spectral separation is utilized, preferably consisting of a curved/spherical-type diffraction grating and (preferably) interference filters and optical sensors.
Accordingly, it is an object of the present invention to address limitations of conventional color/optical measuring techniques.
It is another object of the present invention to provide a method and device useful in measuring the color or other optical characteristics of teeth, fabric or other objects or surfaces with a hand-held probe of practical size that may advantageously utilize, but does not necessarily require, contact with the object or surface.
It is a further object of the present invention to provide a color/optical measurement probe and method that does not require fixed position mechanical mounting, feet or other mechanical impediments.
It is yet another object of the present invention to provide a probe and method useful for measuring color and/or other optical characteristics that may be utilized with a probe simply placed near the surface to be measured.
It is a still further object of the present invention to provide a probe and method that are capable of determining translucency characteristics of the object being measured.
It is a still further object of the present invention to provide a probe and method that are capable of determining translucency characteristics of the object being measured by making measurements from one side of the object.
It is a further object of the present invention to provide a probe and method that are capable of determining surface texture characteristics of the object/tooth being measured.
It is a still further object of the present invention to provide a probe and method that are capable of determining fluorescence characteristics of the object/tooth being measured.
It is yet a further object of the present invention to provide a probe and method that are capable of determining gloss (or degree of specular reflectance) characteristics of the object/tooth being measured.
It is another object of the present invention to provide a probe and method that can measure the area of a small spot singularly, or that also can measure the color of irregular shapes by moving the probe over an area and integrating the color of the entire area.
It is a further object of the present invention to provide a method of measuring the color of teeth and preparing dental prostheses, dentures, intraoral tooth-colored fillings or other materials.
It is yet another object of the present invention to provide a method and apparatus that minimizes contamination problems, while providing a reliable and expedient manner in which to measure teeth and prepare dental prostheses, dentures, intraoral tooth-colored fillings or other materials.
It is an object of the present invention to provide methods of using measured data to implement processes for forming dental prostheses and the like, as well as methods for keeping such measurement and/or other data as part of a patient record database.
It also is an object of the present invention to provide probes and methods for measuring optical characteristics with a probe that is held substantially stationary with respect to the object or tooth being measured.
It is another object the present invention to provide probes, equipment and methods for detecting and preventing counterfeiting or the like by way of measuring or assessing surface or subsurface optical characteristics or features.
Finally, it is an object of the present invention to provide probes and methods for measuring optical characteristics with a probe that may have a removable tip or shield that may be removed for cleaning, disposed after use or the like.